(1) Field of the Invention
This invention relates to a bearing device for use in an internal combustion engine. More particularly, the invention relates to an improved bearing device for an internal combustion engine in which the friction loss of sliding bearings such as crankshaft bearings and connecting rod bearings, that is, the friction loss which is caused to occur around the crankshaft, can be reduced. With the reduction of the friction loss, the needless increase of lubricant oil, the resultant decrease of oil supply to other sliding surfaces and the lowering of oil pressure can well be avoided.
(2) Description of the Prior Art
In order to reduce the friction loss around crankshafts, it is necessary to decrease the friction loss in the bearings that support the crankshafts. Further, it is considered more desirable that the friction loss caused in the connecting rod bearings which are disposed between the crankshaft and the connecting rod ends, is also decreased. However, when viewed from the relation between the friction loss and the clearances of crankshaft bearings, the clearances of sliding bearings for supporting the crankshaft of an internal combustion engine were all set at a constant value in the prior art. The dimension of the clearance was made larger than a certain value so as to avoid seizure between the crankshaft and the sliding bearings, while it was made smaller than the value with which any impact sounds caused by the collision of the crankshaft with sliding bearings were not produced. Such value was determined by experiments. That is, for the purpose of reducing the friction loss, it is desirable that the clearance is set at a value as large as possible. However, when the value of the clearance is set too large, the crankshaft collides violently with the sliding bearings. In other words, the sliding bearings receive impact loads and produce noises. Therefore, the reduction of friction loss had its limit in the conventional art.
Meanwhile, oil reliefs are generally provided in crankshaft bearings and connecting rod bearings, and it is considered that the enlargement of such oil reliefs contributes to the reduction of friction loss in each bearing. However, in the conventional art, the oil reliefs are formed for the purposes of promoting and ensuring the oil circulation. Therefore, the dimension of the oil relief was made about 5 to 15 .mu.m for a crankshaft of 30 to 70 mm in diameter. Such value was considered to be sufficient for the above object. Further, it was believed in the conventional art that, if the dimension of the oil relief is made larger than the above value, the shaft has unnecessary play so that the performance the bearing is affected adversely. Accordingly, it has never been tried to reconsider the set value of the oil relief in order to reduce the friction loss of bearings.